Technology Assessment of Tire Mould Cleaning Systems and Quality Finishing
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International Journal for Quality Research 10(3) 523–546 ISSN 1800-6450 Cristiano Fragassa 1 Martin Ippoliti TECHNOLOGY ASSESSMENT OF TIRE MOULD CLEANING SYSTEMS AND QUALITY FINISHING Article info: Received 06.12.2015 Abstract: A modern tire merges up to 300 different chemical Accepted 07.03.2016 elements, both organic and inorganic, natural and synthetic. UDC – 332.05 During manufacturing, various processes are present such as DOI – 10.18421/IJQR10.03-06 mixing, calendering and extrusion, forming dozens of individual parts. Then, moulding and vulcanization inside special moulds provides the tire its final shape. Since the surface quality of moulds strongly affects the quality of tire, mould cleaning is a fundamental aspect of the whole tire production and cleaning techniques are in continuous development. This investigation proposes a global technology assessment of tire mould cleaning systems including uncommon solutions as multi-axis robots for cleaning on board by laser or dry ice, or ultrasonic cleaning which use cavitation. A specific attention is also focused on the industry adoption of spring-vents in moulds and how they are influencing the development the quality of final products. Keywords: Tire Industry, Moulds, Laser cleaning, Dry ice cleaning, Ultrasonic cleaning, Spring-vents 1. Overview of tire 1 patented its radial tire in 1946 and started the sales since the end of the 40s. Radial tires 1.1. Brief history were used in the US only from the 60s (Eberhart, 1965). The first pneumatic tire was patented by Robert William Thomson in 1845. He also 1.2. Tire types applied for a patent in the US, which he received in 1847 (U.S. Patent No. 5,104, The tires can be classified according to their 1847). This tire, with an inner tube, failed to structure. It is then possible to distinguish 4 replace the solid rubber tire due to resistance types: problems. John Boyd Dunlop, developed a Pneumatic tire: inflated hollow tire, similar but improved pneumatic tire in 1888 retains its shape due to the air pressure, (British Patent No. 10,607, 1888). The radial and equipped with air chamber or tire was patented in 1915 by Arthur W. tubeless (CBP, 2014). Savage (U.S. Patent No. 1,203,910, 1915). Semi-pneumatic tire: hollow tire which After the expiry of Savage’s patent, Michelin is not pressurized. Lightweight, puncture-proof and shock-absorbing, 1 this tire is commonly used, for example, Corresponding author: Cristiano Fragassa email: [email protected] on lawn mowers, shopping carts and wheelbarrows (CBP, 2014). 523 Solid tire: Made by molding, a solid tire To provide traction; is composed of several layers of To ensure stability and directional different thickness and compound, control of the vehicle. which form a composite structure During several decades other characteristics (Figure 1). Steel rings are often used as have been added to these basic functions, on reinforcement (Suripa and demand of the market, such as increased Chaikittiratana, 2008). Solid tires are wear resistance, homogeneous response to among the most important engineering each condition and increasing security. components in heavy industry (Suripa Finally, the tire was expected to contribute to and Chaikittiratana, 2008). They are reducing fuel consumption. As emerged mainly used in forklifts and in various from the research prepared by the Centro Pio types of industrial vehicles, but also on Manzù (1987), this led to a change of karts, scooters and lawn mowers (CBP, perspective, particularly in the automotive 2014). industry. The tire cannot be considered just a mere commodity anymore, but it assumes the role of a real customer technical support. In the automotive sector, the quality of a product does not generally depend only on its performance, but it is a merging of different factors between technological aspects and clients satisfaction (Fragassa et al., 2014). Tires are not an exception, there are no compromises as regards their safety and reliability (Peled, 2015), and they are subject to constant evolution. Figure 1. Cutaway of a solid tire [Courtesy of Continental] Cushion tire: It is a solid tire, however equipped with a sealed internal air space Figure 2. Schematic structure of a radial tire rather than containing pressurized air in [Courtesy of Wikimedia Commons] order to maintain the shape (CBP, 2014). The structure of a tire may vary depending 1.3. Structure of a pneumatic tire on the manufacturer and the intended use. It is possible to identify some basic elements The main functions of a tire are (Gough, (Figure 2): 1981; Peled, 2015): Tread: Part of tire in contact with the To support the weight of the ground. Its surface is suitably shaped vehicle; and can be engraved to improve road To absorb the irregularities of grip and water expulsion (Koštial et al., grounds; 2012). 524 C. Fragassa, M. Ippoliti Steel belts: Reinforcements made of resistance and better high-speed steel wires coated with rubber. They are performance. By contrast, the greater positioned between the carcass and the complexity of construction leads to an tread. Steel belts, crossed with each increase in costs (Lindenmuth, 2006). other, optimizes the directional stability Bias belted tires are bias tires with belts and rolling resistance (Koštial et al., added in the tread region (Lindenmuth, 2012). 2006). Nylon cap: One or two nylon belts Shoulder: Part between the sidewall and placed over the steel belts and inclined the tread. Help maintain a smooth belt at 0° to the rolling direction. They are contour and insulate the body plies from used in high-end tires and should the belt edges (Lindenmuth, 2006). improve the resistance to the speed. Sidewall: It bears most of the weight of Carcass: It bears the inflation pressure. the vehicle and, for this reason, it must By wringing, it transmits forces between be strengthened properly. It also protects the tire and the ground. It consists of the carcass from the weather conditions several crossed plies (Shuy, 1964). Plies (Koštial et al., 2012). are rubber layers with a low elastic Bead chafer: Side part in contact with modulus, which are reinforced by high the wheel’s rim. It partially envelops the modulus cords. These cables can be plies Figure 2 and is mainly made of natural textile, synthetic polymers, metal. It should ensure the adhesion especially Nylon, polyester, Rayon, between tire and wheel and improve air glass fiber or be steel cables (Koštial et tightness. al., 2012; Lindenmuth, 2006; Gough, Bead wire: Ring consisting of bronze- 1981). The number of plies depends on coated or brazed steel wires coated with the type and the size of the tire and by rubber (Koštial et al., 2012; the inflation pressure (Gough, 1981). Lindenmuth, 2006; Shuy, 1964). It Plies are turned around bead (Figure 3). should ensure the coupling between tire The height to which the plies are taken and rim and transmit power. after they have passed round the bead Bead filler: Also called bead apex, its can be low or high, or the plies' characteristics affect handling extremity can extend across together, as (Lindenmuth, 2006). in Figure 4. In this case the plies can be Liner: Inner layer that functions as an arranged to give extra carcass strength inner tube. in the central region of the tire compared with the sidewalls (Gough, 1981). Standard types of tires are diagonal (or “bias”), radial and bias belted (Figure 5). In diagonal or bias tires plies are crossed at 36° (Eberhart, 1965). In radial tires, as suggested by their name, the plies should be positioned radially, thus with an angle of 90° with respect to the rolling direction. As shown in Gough, 1981, this solution will wear poorly because Figure 3. Detail of a typical bead (Gough, the shear modulus of cord-rubber is very 1981) small. The optimum angle is between 70° and 75°. Radial ply tires generate less heat during use, have lower rolling 525 Figure 4. Different plies’ fixing arrangement (V. Gough 1981) Figure 5. Type of tire-casing (Koštial et al, 2012) 1.4. Composition of the compound depends on the intended use of the tire. For example, for a competition car the objective The compound is composed of several may be to optimize performance. For long elements (Table 1), a typical car tire contains distance vehicle, as truck and bus, the usual about 60 raw materials (Lindenmuth, 2006). aim is to minimize the rolling friction, then The compounds can vary depending on the to limit fuel consumption and tire usury. manufacturer and the objective sought, that Table 1. Compound composition (Evans, 2006) Ingredients Car Lorry OTR Rubber/Elastomers 47% 45% 47% Carbon Black 21.5% 22% 22% Metal 16.5% 25% 12% Textile 5.5% -- 12% Zinc Oxide 1% 2% 2% Sulphur 1% 1% 1% Addictives 7.5% 5% 6% Carbon-based materials, total 74% 67% 76% Elastomers: These are materials able to Natural rubber (polyisoprene) is an resume the original shape and size, even if elastomer resulting from the coagulation of greatly deformed by stress, once such stress the latex, an emulsion of aspect sticky has been removed (Campbell, 1963; Mark, proceeds from some tropical plants, typically 1943). They are characterized by a mainly Hevea brasiliensis (Niyogi, 2007a). In the amorphous structure, with low elastic processing of the latex various chemicals are modulus. They can withstand large employed, such as ammonia as a deformations before arriving at break. preservative and formic acid as a coagulant 526 M. Ippoliti, C. Fragassa (Rodgers, 2015; Drury, 2013). Rubber is High static tensile strength (15-22 composed of long, string-shaped chains that MPa); arrange themselves in carbon-hydrogen High elongation (600-900%); bonds (Raja, 1990). Natural rubber has good Excellent elasticity at low abrasion resistance, it is insoluble in many temperature; solvents and has good hysteretic properties, Poor ozone and degradation but is little resistant to fatigue (Rodgers, stability; 2015).